Hopper means having hyperbolic side walls



Feb. 20, 1968 C. E. HULBERT, JR

Filed June 15, 1966 3 Sheets-Sheet l zao /57 X /34 J L 27/ 3/2 /0 V SOL601v 7'ROL 50L .270 RMEL :h= 32 VACUUM PRESSURE X I MBA/V5 I L i I -I 35I CLARENCE E. Hume/7J2 INVENTOR.

ATTORNEY Feb. 20, 1968 c. E. HULBERT, JR 3,369,716

HOPPER MEANS HAVING HYPERBOLIC SIDE WALLS Filed June 15; 1966 5Sheets-Sheet 3 SOL CLARENCE E Hume/w, JR.

1 N VEN TOR.

A TTORNE'Y United States Patent 3,369,716 HOPPER MEANS HAVING HYPERBOLICSIDE WALLS Clarence E. Hulbert, Jr., Houston, Tex., assignor to CapvacIndustries, Inc., Freeport, Tex., a corporation of Texas Filed June 13,1966, Ser. N0. 556,935 4 Claims. (Cl. 222-373) ABSTRACT OF THEDISCLOSURE Apparatus for continuous movement of bulk, granular materialhaving an angle of repose as high as ninety degrees. Said apparatusincludes vessel means having a funnel chamber with an irregular side andcontrol means coupled to said vessel means for controlling vacuum andpressure applied to said vessel means from a vacuum source and apressure source.

This invention pertains generally to bulk material moving apparatus andparticularly to apparatus adapted for moving bulk material, such ashygroscopic. material, which heretofore has not been movable in largevolumes in a rapid manner. The present invention is adaptableparticularly to moving bulk materials, through a wide range of sizes andshapes such as lump coal, gravel, finely ground cake flour, cereals, andlight fluify talc.

The present application is related to my copending application, SerialNumber 463,781, filed June 1-4, 1965, and entitled Abrasive Flow Systemand Methods.

While various means have been employed to move dry materials byconveyor, no known funnel or other device has been capable of providinga fail safe, non-clogging, escape method for dry products to flowthrough metering means, without requiring bin vibrators and shakers toprevent the various materials from bridging, rat holing, clinging, orpacking. The present invention is adaptable for use in a plurality ofconveying functions which will be set forth in the followingdescription.

Among the conveying devices known to applicant are those disclosed inthe following United States Letters Patent:

2,851,553-Grostick, issued September 9, 1958. 2,979,235-Greaves, issuedApril 11, 1961. 3,071,297 Lee, issued January 1, 1963.

Although these patents disclose various means for moving material noneof such patents has provided satisfactory results in certain areas ofmaterial moving. Particularly, sodium chloride, ammonium sulfate andammonium phosphate have been difficult to move with known apparatus andthe rapid moving of this material has been limited generally to beltconveyors or buckets. Such material is in crystal form at roomtemperature and the angle of repose varies from about 30 when dry toabout 85 when moist. Thus, the three mentioned materials along withother members of the alkalyne family of materials exhibit hygroscopicproperties which make these materials very difficult to convey throughknown hoppers and other material moving means. These materials do notlend themselves readily for movement with known apparatus because thematerials surface tension and capillary attraction restricts the fiowthrough hoppers and other mechanism being used for moving the material.

The present invention is adapted for providing a satisfactory solutionto the problems which have heretofore been encountered in the attemptedmovement of various types of material including material havinghygroscopic properties.

3,369,716 Patented Feb. 20, 1968 Thus, it is an object of the presentinvention to provide improved apparatus and methods for the old art offunneling bulk materials from bins, hoppers and the like.

Another object of the present invention is to provide means to employless space distance from the hopper or bin to the outlet by providingtwo dissimilar irregular, curved surfaces.

Still another object of the present invention is to provide an escapemeans for materials whose structure heretofore required shakers orvibrators to provide a substantially constant velocity to the productbeing moved.

Still another object of the present invention is to provide bygravitational force the required energy level necessary by kinematicfunctions, to cause material to flow evenly without restriction due tomass, friction coeflicient, cohesive attraction and molecular structureof such material.

A still further object of the present invention is to provide a means toinsure a material to flow with a near top level attitude, thus allowingmeasuring instruments to obtain accurate data heretofore accomplished byweight controls or inaccurate readings which were the result of theinverted repose angle of the dry product material whose repose anglewould constantly vary in accordance with its ever changing moisturecontent.

Still another object of the present invention is to provide anunrestricted passage of any dry material whose cohesive attraction andsurface tension does not defy the force of gravity and whose mass issuch that it is smaller than the midsection passageway of the device ofthe present invention.

Still another object of the present invention is to provide a constantflow of any material having cohesive strength to metal lower than theweight value of the mass and gravitational force of such material. Forexample, grain and other animal feed products containing molasses andother sticky substances will flow Without restriction when their massand cohesive characteristics fall within the mentioned limits.

Yet another object of the present invention is to provide a universalstructure adaptable for use on various configurations, sizes and typesof material collecting and discharging devices whose characteristicsrequire a constant flow without restriction, are closely coupled andrequire low profile, while utilizing a gravitational discharge method.

In the drawings, FIGURE 1, is a combined side elevational view of thevessel and circuit schematic of the control system of the presentinvention;

FIGURE 2 is a combined funnel shape and chart having curves incorporatedin the present invention plotted on X and Y axes;

FIGURE '3 is a cross-sectional top view of a portion of the curvesincorporated in the present invention taken along line 3-3 of FIGURE 2;

FIGURE 4 is a sectional elevational view of the material mover mechanismof the present invention utilized with a vacuum pump; and

FIGURE 5 is a sectional elevational view of the material mover mechanismof the present invention utilized with a pressure source.

Briefly stated, the present invention includes a method and means forproviding unrestricted uniform feed characteristics to bulk productswhose physical nature has heretofore not been adaptable to existingmethods. It will be appreciated that the principles involved in thepresent inventon may be utilized from the Cartesian curve form to manyshapes and dimensions as long as the primary principles of the presentinvention are maintained, and that the shape shown and described may be'altered in lines of space and configuration. The mathematical functionscontained in the present invention are part of the universal laws ofnature but employed to provide a method and means for dischargingmaterials whose structure and shapes have been difficult to handle.

Referring now'to the drawings in detail, FIGURE 1 is a combined sideview of a vessel and a schematic of the control system of the presentinvention. Vessel means includes an upper semi-spherical portion 134.Generally the interior construction of the vessel means 10 closelyfollows the construction disclosed in my copending United States patentapplication, Serial No. 463,781, filed June 14, 1965, and entitled,Abrasive Flow System and Methods. An inlet 52 is utilized for bringingmaterial into the chamber of vessel means 10.

It will be appreciated that the vessel means 10 explained in detail inmy copending patent application provides a lower material collecting andmetering system chamber. While the device of my copending patentapplication is suitable for the purpose disclosed and claimed therein,the lower material collecting and metering system chamber of my priorcopending application is removed and a hyperbolic mover means issubstituted by connecting to the inner chamber walls to the top sectionof vessel means 10 thereby providing the hyperbolic mover device of thepresent invention with complete access to all materials which pass intothe top inner chamber. The lower opening of hyperbolic mover means canbe connected to a metering valve or rotating feeder valve well known inthe art.

The equipment of the present invention including the hyperbolic movermeans is fully portable and may be mounted on a truck, trailer or skid.

Vessel means 10 has coupled to the upper semi-spherical portion 134 aninlet 52 for material which is fed to the vessel means. A pressurerelief valve 154 is coupled to the semi-spherical portion 134 as is apressure discharge valve 156. The pressure relief valve 154 may bespring loaded and allows the vessel means 10 to vent to the atmosphere.The pressure discharge valve 156 vents to the atmosphere and is coupledthrough lead 157 to a timer housed in control panel 12. Pressuredischarge valve 156 also may be manually operable. An electric motorindicating device 280 is utilized for indicating the upper level ofmaterial positioned in vessel means 10. The electrical motor device 280is coupled through lead 300 to the control panel 12.

A lower level electric motor device 290 is positioned on valve means 10and coupled through lead 302 to control panel 12.

Solenoid 312 is coupled to the vessel means 10 and through lead 314 tothe control panel 12.

Valve 270 and solenoid 271 are coupled to the vessel means 10 andthrough lead 316 to the control panel 12.

Valve 268 and solenoid 269 are coupled through lead 318 to the controlpanel 12.

Vacuum-pressure means 320 is coupled through conduit connecting line 322to valve 279. It will be appreciated that such vacuum-pressure means maybe either a vacuum pump or a pressure device such as a compressor. Aswill be explained subsequently, the vacuumpressure means depends on howthe equipment of the present invention will be used. In one applicationof the invention, both vacuum and pressure is provided alternately andcontinuously.

Generally material enters the vessel means 10 through inlet 52 and isdischarged through valve 268 at the lower portion of the vessel means10. The control panel 12 provides indication and selected actuation ofthe valves as will be explained in greater detail subsequently. Thecontrol panel provides selective control of the components of thepresent invention and may vary in construction according to therequirements of a particular job. It will be appreciated that thematerial inlet 52 may be coupled to suitable means such as hose whichwill allow material to be picked up and moved through the vessel means10.

The valve 268 may be a solenoid actuated valve or a star valve whichallows continuous flow of material through the vessel means 10.

FIGURE 2 is a simplified representation of the curved surfaces and theinterior cylindrical portion of the vessel means of the presentinvention set forth along X and Y coordinates. As shown in FIGURE 2 theX coordinate is horizontal and has been positioned at the junction point50 and 51 of the cylinder wall 38. The Y coordinate has been positionedat the midway point of the diameter of the cylinder formed by wall 38 sothat Y is substantially in the center of the cylinder formed by wall 38.

It will be appreciated therefore that the area designated as I in FIGURE2 is positive in the Cartesian system, area II is negative, area III ispositive and area IV is negative.

The curve designated as A in the accompanying table for curve A is thesame as surface 40 while curve B in the accompanying table for curve Brepresents curved surface 41. Thus, in the tabulation for curve A, sincecurve A lies in area III all value of X and Y are negative. It will beappreciated in reviewing the tabulation for curve A that Y (prime) is 0for the first four readings of X in the right hand portion of the tablefor curve A. As the value of X is 4 in the right hand portion for thetable for curve A, Y is 8 and Y (prime) is 18. Y (prime) is theextention of Y to indicate that there is an intercept or dual value of Ywhen plotting the curve A. As shown in the lower portion of the tablefor curve A, X is positive for areas I and IV and negative for areas IIand III while Y is positive in areas I and II and negative for areas IIIand IV. An important part of the present invention is the fact thatthere is an intercept relationship of the curve A as shown in the tablefor curve A where X is 4, Y is 8 and 18. The fact that there is anintercept indicates that the curve A is not identical or evensubstantially the same as curve B as will be explained subsequently.

Curve B which is the curve portion 41 is tabulated in the table forcurve B and it might be noted that all values for X are positive whileall Y values are negative. The lower portion of the table for curve Bindicates the areas where X and Y are positive and are negative.

It will be appreciated, therefore, that curve A and curve Bare notidentical. The equations for curve A and curve B are not set forth withgreat accuracy although the tables for curve A and the tables for curveB have proven to be satisfactory in practicing the present invention. Itwill be appreciated in viewing FIGURE 2 that curve A and curve B of thepresent invention are not the same in structure, function, or result asthe curved members disclosed in US. Patents 2,979,235 and 3,071,297. The3,071,297 patent specifically discloses a structure wherein there is aconstant decrease in the inner crosssectional area while moving towardthe discharge opening. In the 2,979,235 patent the angle of the bottomwall to the horizontal has been limited to approximately the equivalentor slightly greater than the angle of repose of the material beinghandled. The curves utilized in the present invention are not limited inthe manner set forth in the 2,979,235 and 3,071,297 patents. Thestructure of the present invention allows various types of material tobe readily moved over the curved surfaces 40 and 41 without build-up atany point on the curved surfaces.

As is well known in the bulk material art, the angle of repose of bulkmaterial is the angle, less than ninety degrees, which the slope of bulkmaterial forms with respect to a horizontal plane. In moving bulkmaterial through a conventional funnel the slope of the funnel has aconfiguration substantially the same as the inverted triangle formed bythe two slopes determined by the angle of repose of certain bulkmaterial. The present invention provides two dissimilar, irregularlyshaped mem-- bers which act to provide a varying angle X where X=l80degrees minus (the angle of repose times two).

Referring again to FIGURE 2 it will be seen that the mass of material isgreater along curve B than along curve A in relation to the Y axis.Thus, more compression is forced on the material along surface 41 whilethe lower portion of surface 40 has less compressive force than at anyother portion of the surfaces 40 and 41. The upper portion of surface 49is a slave to the frictional value caused by the repose angle of thematerial moving transverse to the Y axis. It will be appreciated thatthe Y axis is not equidistant from points 43 and 45. Thus, it will beseen that the lower portion of surface 40 provides increased impetus tomaterial moving downwardly. Therefore, the primary object of movingheretofore difiicultto-move-material may be achieved rapidly andeffectively because the lower part of the material is moved by breakingthe center fiow of the material.

FIGURE 3 is a cross-sectional top view taken along line 33 of FIGURE 2to show variations of the curved surfaces. Curved surfaces 40 and 41 areshown coupled to planar members 60 and 62. Points 50. and 51 are shownin FIGURE 3 in broken lines to indicate that surfaces such as 64 and 66might be utilized if the curved portions 40 and 42 are extended topoints 50 and 51. Also, surfaces 68 and 70 might be utilized with thecurved portions 40 and 41. The broken lines shown in FIGURE 3 merely areattempts to indicate that the planar surfaces such as surfaces 60 and 62actually utilized and shown in FIGURES l and 2 are not necessary but maybe of any suitable configuration such as that indicated by surfaces 64and 66 or by surfaces 68 and 70. The only requirement for the curvedsurfaces 40 and 41 of the present invention is that they conformsubstantially to the tables set for curves A and B. Ease of constructionapparently would dictate that surfaces 60 and 62 be planar rather thancurved as shown in the broken lines of curves 64 and 66 and curves 68and 70.

FIGURE 4 is a sectional elevational view of the vessel means utilized inpracticing the present invention when vacuum is provided to such vesselmeans from a vacuum pump (not shown). Vessel means has positionedthereon an inlet 52 which allows material or product to be brought intothe chamber 186 when plunger 256 is opened. Plunger 256 is closed by aircylinder 178 which is coupled to valve 310 operated by solenoid 312. Asexplained previously pressure relief valve 154 is coupled to the uppersemi-spherical chamber 134 and allows venting to the atmosphere of upperouter chamber 144. Discharge line in valve 156 also is positioned onsemispherical portion 134 and allows chamber 144 to be vented toatmosphere when the valve 156 is manually operated. Electric motordevice 280 is coupled through stem 182 to a level control paddle 184 ina manner well known in the art. The level control paddle 184 along withthe electrical device 280 provides a signal for operating air cylinder178 and plunger 256 as explained in my prior copending patentapplication.

Inner suction header 160 extends circumferentially to allow attachmentof filters such as filters 146 and 148. Filters 146 and 148 may beconstructed of perforated pipe having sock covers.

Inner top chamber opening 162 allows communication from the productcollector chamber 186 to the top outer chamber 144 thereby providinginner space dust velocity reduction within the vessel means 10. Acentripetal separator baffle 172 has a centripetal separator ledge 170for air control thereby causing movement of the material within thevessel means 10 to allow the proper movement of material.

Wall 38 defines the inner product collecting chamber 186. Such chamber186 has a semi-spherical upper portion and a cylindrical lower portionand converges downwardly to the outlet 42. Surfaces 40 and 41 providethe downward opening and the configuration of surface 40 6 and 41 hasbeen explained in detail previously in conjunction with FIGURES 2 and 3.v

Disposed below the filters 146 and 148 is an inner filter storage area150 and an inner filter storage area 152.

A paddle 284 is disposed on stem 282 and coupled to electric control290. The paddle 284 and the electrical device 290 provide a signal foractuation of air cylinder 178 in a manner similar to that described inconnection with upper paddle 184 and electric control 280.

A dust door 198 is positioned in surface 40 to allow dust collected inthe inner filter storage area 150 to be passed out of outlet 42 whendust door. 198 is opened by actuation of the control stem 192. Similarlya dust door 202 is positioned in surface 41 to allow dust which has beenaccumulated in dust collection area 152 to be discharged downwardlythrough outlet 42 upon actuation of stem 196.

The vessel means 10 may be positioned on a suitable frame 292 withrivets or bolts such as 294 and 296.

A star valve 266 may be positioned within housing 268 to allowcommunication of outlet 42 with a pressurized material collecting pan234 coupled to outlet line 16. Inlet line 22 is in communication withproduct collecting pan 234 and outlet 16. The star valve 266 may be ofany type well known in the material handling art. Such valve is arotating bulk product material feeder valve for measuring the productdischarge and for supplying an air lock from product collecting pan 234.

The vessel means 10 shown in FIGURE 4 is utilized with a vacuum pumpcoupled to valve 270 which has solenoid 271 coupled thereto. Valve 270is coupled to elbow 158 which is in communication with the inner suctionheaded 160. Valve 270 is a multiport valve which may for example be aRockwell-Nordstrom Valve arrangement No. l-three way, two port, degreeturn, two position valve. Valve 270 is operated by air cylinder having atwo position stroke. The air cylinder of valve 270 is actuated by an airelectric solenoid valve. In position No. 1 wherein vacuum is utilizedthe air cylinder to air cylinder unit 178 opens and .valve 270 opens tothe vacuum pump by the solenoid signal. In position No. 2 during thepressure cycle the air cylinder 178 closes and valve 270 closes tovacuum supply but opens to pressure. The return to vacuum is controlledby a timer device which opens vessel pressure discharge valve 156 toatmosphere to release the pressure which has built up in the vessel.When the pressure within the vessel has been vented to atmospherethrough the vessel pressure discharge valve 156, another signal istransmitted to the solenoid operating valve 270 and to the solenoidoperating air cylinder 178. Thus it will be apparent from the aboveexplanation that the sequence of operation of the vessel means 10 when astar valve 266 is utilized will be such that the movement of materialthrough the outlet 42 will be continuous. As explained previously FIGURE4 shows the vessel means of the present invention adapted for use with avacuum pump (not shown) which may be coupled to the valve 270 in amanner well known to those skilled in the vessel art in the materialmoving art. While operating with a vacuum pump as shown in FIGURE 4, theupper electrical control unit 280 will cut off the vacuum pump in theevent that too much material is stored in the chamber 186. The lowerelectrical control unit 290* will actuate the vacuum pump when thematerial in chamber 186 falls below the level of paddle 284.

Referring again to FIGURES 2 and 3, it will be apparent from theconfiguration of surfaces 40 and 41 that material which is being broughtinto the inner product collecting chamber 186 is positioned alongmembers 40 and 41. The configuration of these members is such that thematerial flow downwardly through outlet 42 is continuous and may allowmany different kinds of material to be effectively dischargedv from thevessel and move through the outlet 16. The configuration of members 40and 41 prevents rat holing or material accumulation along such memberseven though the material which is being moved may possess stickycharacteristics which have heretofore prohibited or limited massmovement thereof.

Thus it will be apparent from the foregoing explanation of FIGURE 4 thatFIGURE 4 represents one embodiment of the present invention with valve270 positioned for coupling to a vacuum pump. The star valve 266provides continuous flow of material which is brought in through inlet52 from outlet 42.

FIGURE is a cross-sectional elevational view of the vessel meansutilized with a pressure source coupled to valve 270 after valve 270 isrotated 90 degrees. The valve utilized with the embodiment shown inFIGURE 5 may be a full bore pattern two way, hard surface valve whichmay be manually operated or operated by an air cylinder. Member 269opens and closes the outlet 42 with respect to the product collectingpan 234.

Thus it will be apparent in reviewing FIGURE 5 that when presure isutilized on the vessel means 10 through valve 270, that the air cylinder178 operates rubber plunger 256 to periodically discharge material whichhas been accumulated within chamber 186 through operation of the levelindicator devices having paddles 184 and 234. For example, member 269will be closed during a filling cycle while the air cylinder 178provides downward movement of plunger 256 to allow material to bebrought in through inlet 52 to the product accumulation chamber 186while vacuum is provided. As material accumulates within the chamber 186and as the paddle on the upper level indicator is actuated, plunger 256is actuated by the air cylinder 178 to close the inlet 52 and the member269 is opened to allow discharge of the material which has beenaccumulated in chamber 186. Also pressure is applied to the chamber 186through valve 270 which was actuated by upper level controller 280 todischarge the material in chamber 186.

Paddle 284 actuates a timer device in the control panel 12 and a signalis provided to open the upper discharge valve 156 to release pressurewithin vessel means 10 dropping the pressure within vessel means 10 toatmospheric pressure after a brief interval of time, which may be on theorder of several seconds, the timer device provides a pneumatic signalto close valves 269 and 156 and actuates air cylinder 178 to openplunger 256 and allows valve 290 to be coupled to a vacuum pump. Vacuumis provided to the vessel means 10 until the above action is repeated.The operation of the vessel means 10 as shown in FIGURE 5 includes apressure source such as an air compressor and vacuum source such as avacuum pump. The pressure and vacuum act together on an alternate basisto move material in the vessel means 10.

As explained previously in conjunction with FIGURE 4 the vessel means 10allows movement of heretofore unmovable material or material which hasbeen difficult to move without the problems previously encountered. Theoperation of the vessel means 10 is achieved through coordinatedoperation of member 269, plunger 256 and pressure relief valve 156.

While my prior copending patent application provided means for conveyingvarious material by positive and negative pressure it will now beappreciated that the present invention will move material heretoforediflicult to move by pneumatic conveyor means.

By incorporating the hyperbolic mover of the present invention thedisclosure of my copending application it is now possible to movehygroscopic materials such as fertilizer in bulk at very high quantitythus economically allowing loading and unloading of ships, barges,railroad cars, and other storage facilities.

It will be appreciated that the principles involved in the presentinvention when incorporated with my original vessel means will serve adual function by being available to unload material from ships, barges,railroad cars,

bulk storage systems and convey such material to other suitable storagemeans, or to measure, weigh and convey by metered volumes said materialto any point for use in blending or manufacturing other products.

The present invention utilizes heretofore unavailable pneumaticprinciples to provide satisfactory means for the movement of any bulkmaterial. It will capture all the product dust and return it into theproduct collecting point or capture the dust for other purposes.

Through pneumatic conveying at high pressure of abrasive materials asset forth in my prior copending application it is also possible toconvey these abrasive materials whose characteristics are hygroscopic orother materials that contain a high moisture saturation that have beenin the past very difficult to convey.

Although preferred embodiments of the invention have been shown anddescribed, it will be apparent to those skilled in the art of vesselconstruction and pneumatic conveying that many modifications may be madeof the present invention without departing from the spirit of theinvention as defined by the following claims. Although such claims arepresented in indented format to facilitate reading and understandingthereof, such indented format is not to be construed as a structural orfunctional limitation of the elements or steps related in such claims.

FOR CURVE A Upper Iimi.X-=O Y=0 Lover Iimi. as X a reach s 0 (Y 21 or:

(Y .8 5 D.a. of

Note: All valies of it & are negative x Y x Y Y II I H H) q... x x --bIII IV I m i FOR CURVE "B" UJper Limit X D Y kwer: Limit x .7 Y 21 NoteX values Are all POSLtiVE Y Are all Negative X Y I X Y Q- X x I claim:

1. A system for continuously moving bulk material, said system includingin combination vessel means having an inlet and an outlet for the bulkmaterial, said vessel means including a chamber having first and secondcurved surfaces, said first curved surface and said second curvedsurface originating on substantially the same horizontal plane andconverging downwardly whereby said first curved surface followssubstantially the shape of a hyperbola and said second curved surfacefollows substantially the shape of an irregular hyperbola so that theweight of the bulk, granular material at any point on a horizontal planethrough said first curved surface and through said second curved surfaceis considerably greater on the said second curved surface than on thesaid first curved surface, said first and second curved surfaces havebeginning points on a substantially horizontal plane equidistant from asubstanttially vertical plane with the middle lower portion and endingpoints of said first and second curved surfaces having differentdistances from said vertical plane whereby bulk material having a highangle of repose will move by gravity along said first and second curvedsurfaces, and

vacuum-pressure means coupled to said vessel means for providingselected pressure and vacuum to said vessel means.

2. A system defined by claim 1 wherein a source of bulk material havinga high angle of repose is included in said combination.

3. A system defined by claim 1 wherein said vessel means includes avalve having an open position and a closed position in communicationwith said outlet, and said vacuum-pressure means includes a vacuum pumpand a compressor selectively and periodically in communication with saidvessel means.

4. A hopper for continuously moving by gravity bulk, granular materialhaving an angle of repose as great as ninety degrees, said hopperincluding in combination first, second, and third curved surfaces eachhaving substantially the shape of a hyperbola with said second curvedsurface being intermediate said first and said third curved surfaces,and a fourth curved surface intermediate said first curved surface andsaid third curved surface, said fourth curved surfacing having avertical directrix determined by a point on any horizontal plane passingthrough said first, second, third and fourth curved surfaces with saidpoint being the corner nearest the center of said horizontal plane of animaginary square formed on said horizontal plane with said square havingan area equal to substantially one-fourth of the total area of saidhorizontal plane bounded by said first, second, third and fourth curvedsurfaces.

References Cited UNITED STATES PATENTS 410,116 8/1889 Richards 222-561,052,653 2/1913 Crowley 222-194 X 2,590,458 3/ 1952 Prickett 222-2,636,208 4/ 1953 Leeper 222-462 X 2,694,415 11/1954 Green 222-460 X2,851,553 9/1958 Grostrick 340-246 X 2,979,235 4/1961 Greaves 222-1853,071,297 1/1963 Lee 222-462 3,110,420 11/ 1963 Brewer 222-56 3,159,31412/1964 De Lucca 222-460 X 3,198,366 8/ 1965 Hartley 222-56 3,212,67110/1965 Rock 222-56 3,217,927 11/1965 Bale et a1 222-56 3,253,745 5/1966 Skelton 222-56 WALTER SOBIN, Primary Examiner.

